It is unnecessary maintaining a list of parameters which require a
restart, as you can tell by looking at pg_settings.
The way I do it is by comparing the contents of pg_settings with a
snapshot I made just after (or just before) the server was last
restarted. If any settings have been changed that have a context of
'postmaster', the server needs a restart.
It's not as easy as it sounds to do that with Ansible, since you don't magically get a list of parameters which are changed from last time. All parameters are in a template which generates postgresql.conf, so you just get the information that that file changed, that is why you need to compare each parameter separately. Since it is a lot faster to compare just a few parameters which we set that require a restart, it is worth keeping a list.
If anyone is interested this is how I detect if a server needs a restart. I define a dict with parameters that require a restart and set the keys to have values of the current variables:
postgres__restart_params:
listen_addresses: "{{ postgres_listen_addresses }}"
port: "{{ postgres_port }}"
max_connections: "{{ postgres_max_connections }}"
superuser_reserved_connections: "{{ postgres_superuser_reserved_connections }}"
wal_level: "{{ postgres_wal_level }}"
fsync: "{{ postgres_fsync }}"
max_wal_senders: "{{ postgres_max_wal_senders }}"
hot_standby: "{{ postgres_hot_standby }}"
shared_buffers: "{{ postgres_shared_buffers }}"
archive_mode: "{{ postgres_archive_mode }}"
postgres__restart_params:
listen_addresses: "{{ postgres_listen_addresses }}"
port: "{{ postgres_port }}"
max_connections: "{{ postgres_max_connections }}"
superuser_reserved_connections: "{{ postgres_superuser_reserved_connections }}"
wal_level: "{{ postgres_wal_level }}"
fsync: "{{ postgres_fsync }}"
max_wal_senders: "{{ postgres_max_wal_senders }}"
hot_standby: "{{ postgres_hot_standby }}"
shared_buffers: "{{ postgres_shared_buffers }}"
archive_mode: "{{ postgres_archive_mode }}"
then I check this in the following task:
- name: Check if a postgres restart is required on master
command: psql -p {{ postgres_port }} -At -U postgres -c "SELECT current_setting('{{ item.key }}') <> '{{ item.value }}';"
with_dict: postgres__restart_params
register: restart_params
always_run: yes
ignore_errors: yes
changed_when: restart_params.stdout == 't' or restart_params|failed
notify: restart postgres
- name: Check if a postgres restart is required on master
command: psql -p {{ postgres_port }} -At -U postgres -c "SELECT current_setting('{{ item.key }}') <> '{{ item.value }}';"
with_dict: postgres__restart_params
register: restart_params
always_run: yes
ignore_errors: yes
changed_when: restart_params.stdout == 't' or restart_params|failed
notify: restart postgres
ignore_errors is needed since when changing port, psql cannot connect, so when that happens I also restart.
